Not applicable.
(1) Field of the Invention
The present invention relates to antennas and, more particularly, to a digital goniometer especially suitable for controlling a steerable antenna pattern from two orthogonal antennas over the VLF/LF communications band.
(2) Description of the Prior Art
Submarine antenna systems may frequently utilize the VLF/LF communications band (8 kHz-200 kHz) by means of two magnetic loop antennas which may be referred to as a multifunction antenna. The two magnetic loop antennas are preferably identical and aligned perpendicular to each other in one housing. One loop is referred to as the Fore and Aft (F/A) antenna. The other loop is referred to as the Athwartships (ATH) antenna. The multifunction antenna does not rotate, and there are null spots where the antenna gain is near zero. Orienting this null spot toward a source of interference is desirable to reduce the received interference. Likewise, orienting the highest gain region of the antenna toward the desired signal is also desirable. Currently, an analog mechanical device is used to combine the F/A signal with the ATH signal in order to obtain the desired orientation. The mechanical device contains a stator for each loop and a rotor that can be rotated to adjust the proportional contribution of each loop. The device employs Faraday""s Law of Induction for its operation. The mechanical device presently utilized is an electromechanical resolver often known as a goniometer. While goniometers may be utilized to achieve other effects and functions, a goniometer may also be utilized for steering a figure-eight antenna pattern with two identical orthogonal antennas by mechanical means.
It would be desirable to provide a more accurate, lightweight, compact, antenna goniometer that does not require elaborate external drive circuitry and has no moving parts.
Patents that show attempts to solve the above and other related problems are as follows:
U.S. Pat. No. 5,402,132, issued Mar. 28, 1995, to Hall et al., discloses a direction finding system utilizing a single monopole/crossed slot antenna in combination with associated electronic circuitry. Each of the four ports of the antenna are connected to amplitude varying elements whose outputs are combined by a power combiner. A microcontroller stores the signal. The microcontroller also generates the signals which control the amplitude variation supplied by each of the amplitude varying elements. Two configurations of the amplitude varying elements are provided by predetermined settings within the microcontroller. The two settings are selected to configure the antenna on two distinct reception patterns, each with a predetermined angular offset from a reference direction. In operation the antenna will be configured for a first reception pattern. The signals received will be detected, quantified, and stored by the microcontroller which subsequently reconfigures the antenna for a second reception pattern. A second signal is received by the antenna in the second configuration and again is detected, quantified, and stored by the microcontroller. The microcontroller determines the difference between the two signals and, based upon a predetermined calibration curve relating differences in the stored signals to the angle of arrival of the signals from the reference direction, determines the angle from which the signal arrived.
U.S. Pat. No. 6,160,519, issued Dec. 12, 2000, to Christian O. Hemmi, discloses a two-dimensionally steered antenna system including a planar lensing system operable to focus signals received from a plurality of ground-based cells. A first steering system is operable to steer a beam for each ground-based cell in a first direction by weighing signals associated with the ground-based cell based on a position of the antenna system relative to the ground-based cell in the first direction. A second steering system is operable to steer the beam for each ground-based cell in a second direction by weighing signals associated with the ground-based cell based on a position of the antenna system relative to the ground-based cell in the second direction.
U.S. Pat. No. 4,150,382, issued Apr. 17, 1979, to Ray J. King, discloses an invention which provides a guided wave antenna having a radiation pattern which can be controlled electronically, by control signals derived from a computer or any other suitable source. In this way, the directional characteristics of the antenna can be adjusted and/or scanned rapidly, without any mechanical manipulation of the antenna. In one embodiment, a guided radio wave is launched along an antenna surface having an array of elements which provide variable non-uniform surface impedance adapted to be controlled by electronic signals. For example, each variable impedance element may comprise a wave guide section having one end leading from the antenna surface. Each wave guide section may include a solid-state electronic reflection amplifier having characteristics which can be varied by supplying control signals to the amplifier, to vary the magnitude and phase angle of the wave reflected from the reflection amplifier. By changing the control signals supplied to any particular reflection amplifier, it is possible to cause attenuation or amplification and phase shift of the guided wave as it passes across the particular wave guide section. A wide variety of solid-state electronic control elements may be provided along one or more surfaces of the antenna. In another embodiment, a wave traveling in a closed subsurface wave guide is coupled into the guided wave open surface structure, using an array of wave guide elements containing electronically controllable amplifiers and phase shifters.
U.S. Pat. No. 5,714,961, issued Feb. 3, 1998, to Kot et al., discloses a directional planar antenna. The antenna has an array of coaxial ring-slot radiating elements formed through a conductive layer on a dielectric substrate. A number of probes, coupled to the ring-slot elements, selectively excite a separate resonant mode on each ring-slot element. The resonant mode supported by a ring-slot element depends upon the geometry of that ring-slot element. The resonant modes combine in the far field to form a radiation pattern directional in azimuth and elevation. By adjustment of the relative phase difference or relative amplitude between the excited modes, the radiation pattern can be steered.
The above-cited prior art does not show a suitable lightweight, compact antenna goniometer with non-moving components utilizing two orthogonal antennas that is operable for steering a figure-eight antenna pattern. Those skilled in the art will appreciate the present invention that addresses the above and other problems.
Accordingly, it is an object of the present invention to provide an improved antenna goniometer.
It is another object of the present invention to provide an antenna goniometer operable with two orthogonal antennas for steering a figure-eight antenna pattern.
An advantage of a system in accord with the present invention is an antenna goniometer that can be operated in a fully automated manner that can be controlled from software.
In accordance with the present invention, a VLF/LF communications antenna goniometer for a first antenna loop and a second antenna loop is provided that is operable for controlling an angular orientation of a figure-eight antenna reception pattern for the first antenna loop and the second antenna loop. The preferred embodiment shows first and second antennas which are orthogonal with respect to each other; however, the teachings of this invention can be applied by one of ordinary skill in the art to other antenna configurations. The goniometer comprises one or more elements such as, for instance, a first variable gain amplifier for a first signal produced utilizing the first antenna wherein the first variable gain amplifier has a first output, a first data register for storing a digital value related to a first gain setting for the first variable gain amplifier such that the first gain setting is related to the angular orientation, a second variable gain amplifier for the second antenna for a second signal produced utilizing the second antenna wherein the second variable gain amplifier has a second output, a second data register for storing a digital value related to a second gain setting for the second variable gain amplifier such that the second gain setting is related to the angular orientation, and a summing amplifier for combining the first output and the second output.
Other elements of the goniometer may comprise a first digital data link for supplying the first gain setting to the first data register and a second digital data link for supplying the second gain setting to the second data register. In the preferred embodiment, the first gain setting is a sine function related to the angular orientation, and the second gain setting is a cosine function related to the angular orientation.
The goniometer may further comprise an inverter for inverting at least one of the first signal or the second signal. The summing amplifier adds the first output and the second output together.
In operation, a method is provided for controlling an antenna reception pattern for the first antenna and second antenna wherein the method comprises one or more steps such as, for instance, producing a first antenna signal utilizing the first antenna, producing a second antenna signal utilizing the second antenna, determining a first gain signal related to a desired antenna reception pattern, determining a second gain setting related to the desired antenna reception pattern, digitally adjusting the first gain setting for the first antenna signal to produce a first antenna processed signal, digitally adjusting the second gain setting for the second antenna signal to produce a second antenna processed signal, and combining the first antenna processed signal and the second antenna processed signal. Additional steps may include determining the first gain signal and the second gain signal to produce a figure-eight reception pattern having a desired angular orientation.
Other method steps may include providing that the first antenna signal and the second antenna signal are substantially in phase with each other to produce a figure-eight pattern. Additional steps may include utilizing software to adjust the first gain setting and the second gain setting.
In more detail, the method may comprise controlling a first magnitude of the first antenna signal with the first gain setting to produce the first antenna processed signal, and controlling a second magnitude of the second antenna signal with the second gain setting to produce the second antenna processed signal and/or providing that the first gain setting is related to a sine function of an angular orientation of a figure-eight reception pattern, and providing the second gain setting is related to a cosine function of the angular orientation of the figure-eight reception pattern.
In other words, a method is provided to produce a figure-eight antenna pattern with a selected angular orientation comprising one or more steps such as, for instance, providing that a first antenna signal and a second antenna signal are substantially in phase with respect to each other, and digitally controlling a first magnitude of the first antenna signal and a second magnitude of the second antenna signal such that the first magnitude is related to a sine function of the angular orientation and the second magnitude is related to cosine function of the angular orientation. Other method steps then include combining the first antenna signal with the second antenna signal. The combining may further comprise summing the first antenna signal to the second antenna signal. Preferably the method comprises utilizing software to compute a first gain setting for the first magnitude and a second gain setting for the second magnitude, storing the first gain setting in a first register and storing the second gain setting in a second register. Preferably the method permits for dynamically changing the angular orientation utilizing software.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. It will be understood that above listed objects and advantages of the invention are intended only as an aid in understanding aspects of the invention, are not intended to limit the invention in any way, and do not form a comprehensive list of objects, features, and advantages.